Method of drying lumber

ABSTRACT

A method of drying lumber in a single chamber comprising the combination of a steam heating step, a hot air heating/drying step and a vacuum drying step.

United States Patent Nakayashiki Nov. 25, 1975 [54] METHOD OF DRYINGLUMBER 1,763,070 6/1930 Shinn 34/165 1,778,079 10 1930 K t 34 16.5 X[75] Inventor: Ken l Nakayashflu, Oita, Japan I emson [73] Assignee:Seiwa Kosan, Ltd., Osaka, Japan 22 Filed: 2 1974 Primary ExaminerJohn J.Camby Attorney, Agent, or Firm-Sughrue, Rothwell. Mion, [21] Appl. N0.:500,767 Zinn & Macpeak [30] Foreign Applieation Priority Data Aug. 24,1973 Japan 48-95365 ABSTRACT [52] U.S. C1. 34/l3.8; 34/165 [51] Int. Cl.F26B 7/00 58 Field 01 Search 34/134, 13.8, 16.5 A method of drymg umberSmg'e Chamber prising the combination of a steam heating step. a hot[56] References Cited air heating/drying step and a vacuum drying step.

7 UNITED STATES PATENTS 1,050,151 1/1913 Loomis 34/13.4 7 Claims, 2Drawing Figures US. Patent Nov. 25, 1975 3,921,309

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METHOD OF DRYING LUMBER BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to a method of drying lumber.

2. Description of the Prior Art Industrially employed methods of dryinglumber include seasoning in the open air and in kilns. However, thedrawbacks of known methods are that a long period of time is required,and further that splitting and/or warping occur frequently. A more rapiddrying method where splitting rarely occurs is described in JapanesePatent Publication Laid-Open No. 33001/1973, wherein green lumber isdried by blowing steam through a sealed tank in which the lumber to bedried is placed, evacuating the tank to reduce the moisture content tosome degree, transferring the lumber so treated to a sealable chamber,and blowing hot air through the chamber. This method can, indeed, beapplied to relatively thin lumber (less than about mm thick), but, inorder to dry thicker lumber, a fairly long time is required, and qualitydeterioration will occur frequently clue to splitting, warping and thelike.

SUMMARY OF THE INVENTION This invention provides an improved method ofdrying lumber, comprising:

1. blowing steam through a hermetically sealable chamber containing thelumber to be dried;

2. blowing hot air through the hermetically sealable chamber;

3; evacuating the hermetically sealable chamber;

4. repeating steps (2) and (3) alternately at least once; and

5. repeating at least once the sequence of steps (I),

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS FIGS. 1 and 2 eachillustrates an apparatus for conducting an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION This invention has an advantagethat the drying steps can be accomplished in one and the same chamberfrom the beginning to the end.

The method of drying lumber of the present invention will be explainedby the accompanying drawings in which FIGS. 1 and 2 eachdiagrammatically illustrates an apparatus for conducting an embodimentof the basic concept of the invention.

The lumber l to be dried is placed in hermetically sealable chamber 2,and steam is blown through the chamber from the steam blowing pipe 3.Condensed moisture is removed through steam trap 4. This blowing ofsteam provides a disinfection, but the frequency of conducting this stepmust be much smaller in comparison with that of the blowing of hot airand vacuum drying presented hereinbelow. The fan 5 is then switched on,and hot air is introduced in the chamber 2 through air heater 6 via hotair conducts 7 and 8. The vacuum pump 9 is switched on to evacuate thechamber 2, through vacuum exhaust 13 via conducts l0 and 11 andcondenser 12. The condenser 12, through which cold water is circulated,is arranged in order to effectively collect the vapor in the chamber 2and lighten the burden of the vacuum pump 9. The hot air can becirculated as shown in FIG. 2. In this case, the surface of the lumberis maintained in a damp condition, and therefore, splitting and warpingoccur less frequently. By the specific combination of the steps asdescribed above, lumber having a high moisture content and largethickness can be dried in a short time with splitting and warpingoccurring rarely. The air heater 6 may be arranged inside the chamber 2,if desired, FIG. 2 shows air return 14 for recirculation of the hot air.

Thus, the present invention provides a method of drying lumber, in whichvacuum drying can be performed at an extremely low temperature byevacuating a chamber containing the lumber to be dried as highly aspossible, after blowing steam and hot air through the chamber totransfer the latent heat of vaporization to the lumber by convection.For example. when the vacuum drying step is operated at 20 mm Hg (abs),the temperature need only lie above the saturation temperature at thatpressure, about 20C.

Preferred embodiments of the invention are summarized below, and.depending on the species of wood, board thickness, conditions of growth,initial moisture content and the like, optimum conditions can beselected from the following operating conditions:

1. steam blow: about 100C for about 0.5 to 1 hour 2. hot air blow: about60 to C for about 0.5 to 1 hour I 3. vacuum drying: about 10 to 60 mm Hgfor about 0.25 to 2 hours. After step (1), steps (2) and (3) arerepeated alternately three to eight times, preferably four or fivetimes. Step (1) is then repeated, and steps (2) and (3) are repeated asmentioned above. The series of these steps is repeated about four to 20times in total. Satisfactory results are not obtained due to frequentoccurrence of splitting and warping, if step (1) is not operated atregular intervals between the repetition of steps (2) and (3).

The following examples are given to facilitate a more detailed andbetter understanding of the present invention, the invention is not tobe construed as being limitecl by these examples. All percents are byweight.

EXAMPLE 1 One hundred elm boards (90 X 300 X 2000 mm: initial moisturecontent: 30-60 percent were placed in piles in a chamber 2 of the typedescribed in FIG. 1 having a volume of 30 m at vertical intervals of 3cm and at horizontal intervals of 1 cm between the boards. The boardswere dried according to the following procedures:

Operating Conditions 1. Steam Blow: C, 0.5 hour 2. Hot Air Blow: 60C,0.5 hour 3. Vacuum Drying: 20 mm Hg, 2 hours After step (1 steps (2) and(3) were repeated alternately four times. The series of these steps wasrepeated 12 times in total. The treated boards had a moisture content ofabout 0 to 10 percent.

In order to obtain the same result in terms of dryness as in Example 1,known methods require about 6 months using open air seasoning. andsubsequently about 1 month using kiln seasoning.

EXAMPLE 2 Three hundred elm boards (50 X 300 X 2000 mm; initial moisturecontent: 60-80 percent) were arranged in EXAMPLE 3 Two hundred and fiftyelm boards (50 X 380 X 2600 mm; initial moisture content: 100-120percent) were arranged in a similar manner to the arrangement in Examplel in a chamber 2 of the type shown in FIG. 2 having a volume of 90 m Theboards were dried according to the following procedures:

Operating Conditions 1. Steam Blow: 100C. 1 hour 2. Hot Air Blow: 6090C.0.5 hour 3. Vacuum Drying: mm Hg. 1 hour After step l steps (2) and (3)were repeated alternately five times. The series of these steps wasrepeated 20 times in total. The treated boards had a moisture content of8 to 12 percent.

Although the present invention has been described in detail and withreference to specific embodiments thereof, various changes andmodifications can be 4 made therein by one skilled in the art withoutdeparting from the spirit and scope thereof.

What is claimed is: I

l. A method of drying lumber, comprising the steps of:

l. blowing steam through a hermetically scalable chamber in which thelumber to be dried is placed;

2. blowing hot air at a temperature of between about 60 to about Cthrough said chamber;

3. evacuating said chamber;

4. repeating steps (2) and (3) alternately at least once; and

5. repeating at least once the sequence of steps l (2), (3) and (4).

2. The method as claimed in claim 1, wherein step (4) is repeated threeto eight times and step (5) is repeated four to 20 times.

3. The method as claimed in claim 1, wherein in step (1 said steam is ata temperature of about C and the blowing of said steam is for about 0.5to 1 hour, in step (2) the blowing is for about 0.5 to 1 hour, and instep (3) said chamber is evacuated to a pressure of about 10 to 60 mm Hgand maintained evacuated for about 0.25 to 2 hours.

4. The method as claimed in claim 1, wherein in step (2) said air iscirculated. v

5. The method as claimed in claim 1, wherein in step (1 the steamemployed is at a temperature of about 100C such that it is almostsaturated with water.

6. The method as claimed in claim 1, wherein in step (3) said evacuatingis conducted at about 10 to about 60 mm Hg.

7. The method as claimed in claim 1, wherein saaid method consistsessentially of said steps (1) (5).

1. A method of drying lumber, comprising the steps of:
 1. blowing steam through a hermetically sealable chamber in which the lumber to be dried is placed;
 2. blowing hot air at a temperature of between about 60* to about 90*C through said chamber;
 3. evacuating said chamber;
 4. repeating steps (2) and (3) alternately at least once; and
 5. repeating at least once the sequence of steps (1), (2), (3) and (4).
 2. blowing hot air at a temperature of between about 60* to about 90*C through said chamber;
 2. The method as claimed in claim 1, wherein step (4) is repeated three to eight times and step (5) is repeated four to 20 times.
 3. The method as claimed in claim 1, wherein in step (1) said steam is at a temperature of about 100*C and the blowing of said steam is for about 0.5 to 1 hour, in step (2) the blowing is for about 0.5 to 1 hour, and in step (3) said chamber is evacuated to a pressure of about 10 to 60 mm Hg and maintained evacuated for about 0.25 to 2 hours.
 3. evacuating said chamber;
 4. repeating steps (2) and (3) alternately at least once; and
 4. The method as claimed in claim 1, wherein in step (2) said air is circulated.
 5. The method as claimed in claim 1, wherein in step (1) the steam employed is at a temperature of about 100*C such that it is almost saturated with water.
 5. repeating at least once the sequence of steps (1), (2), (3) and (4).
 6. The method as claimed in claim 1, wherein in step (3) said evacuating is conducted at about 10 to about 60 mm Hg.
 7. The method as claimed in claim 1, wherein saaid method consists essentially of said steps (1) - (5). 